Liquid crystal display and method of manufacturing the same

ABSTRACT

Upper electrodes ( 10, 11 ) and lower electrodes ( 2 ) formed on a substrate ( 1 ) of a liquid crystal display are disposed so as to cross each other, and two nonlinear resistance elements ( 13, 14 ) are constituted by each of the upper electrodes, an insulation film, and each of the lower electrodes. One of the upper electrodes constituting the nonlinear resistance elements is connected with a signal electrode ( 9 ), and the other with one of the display electrodes ( 12 ) constituting display pixels. Connection portions ( 4 ) connecting an anodic oxidation electrode ( 3 ) with each of the lower electrodes ( 2 ) are split in parts of regions thereof such that the lower electrodes ( 2 ) each resembling an island in shape are formed, and each of the display electrodes is provided with an overlapping portion  15  thereunder, partially overlapped with each of the connection portions ( 4 ) where a double layer film consisting of a metal film and an insulation film is left intact. 
     In the liquid crystal display constituted as above, an asymmetrical current-voltage characteristic thereof due to a voltage applied to the signal electrode ( 9 ) is turned symmetrical, and a d-c voltage component applied to a liquid crystal layer is reduced, preventing deterioration in the quality of liquid crystal and the contrast of display, and occurrence of a flicker phenomenon and an image sticking, that is, after-image phenomenon.

This application is a division of prior application Ser. No. 08/765,434filed Jan. 14, 1997, which is a national stage application under § 371of international application PCT/JP95/01412 filed Jul. 14, 1995 now U.S.Pat. No. 5,893,621.

TECHNICAL FIELD

The present invention relates to a liquid crystal display comprising MIMelements composed of metal-insulator-metal structures ormetal-insulator-transparent and electrical conductor structures, and amethod of manufacturing the same.

BACKGROUND TECHNOLOGY

Along with an advance in commercial application of liquid crystaldisplays, liquid crystal displays of an active matrix type capable ofdisplaying images of excellent quality have come by now to occupy aposition in the mainstream of the market.

The active matrix type liquid crystal display described above comprisesthin-film transistors (TFTs), diodes, or nonlinear resistance elementsof a metal-insulator-metal (referred to hereinafter as “MIM”) structurecomposed of three layers consisting of metal-insulator-metal ormetal-insulator-transparent and electrical conductor, as switchingelements for each of liquid crystal display electrodes for displayingimages.

The MIM elements described above is generally composed of a Ta—Ta₂O₅—Cror Ta—Ta₂O₅-ITO structure. Herein, Ta refers to a tantalum film, Ta₂O₅ atantalum oxide film, Cr a chromium film, and ITO an indium tin oxidefilm.

With a liquid crystal display using MIM elements, images are displayedby switching on and off a liquid crystal layer connected in series withthe MIM elements by taking advantage of a nonlinear voltage-currentcharacteristic of the MIM elements.

Now referring to FIGS. 29 to 32, the structure of a conventional liquidcrystal display panel having nonlinear resistance elements composed ofthe Ta—Ta₂O₅-ITO structure is described hereafter.

As shown clearly in FIG. 32, the MIM element comprises a tantalum (Ta)film as a lower electrode 103 formed on a first substrate 102, atantalum oxide (Ta₂O₅) film as an insulation film 104 formed on thelower electrode, and a transparent and electrically conductive film 10composed of an indium tin oxide (ITO) film as an upper electrode 105formed on the insulation film, all these films together constituting anonlinear resistance element.

In addition, the MIM element is provided with a display electrode 106composed of an indium tin oxide film. Data signals dependent on thecontents of display are applied on the display electrode 106 via thenonlinear resistance element by a signal electrode 107 composed of atantalum film and a tantalum oxide film.

This liquid crystal display is provided with the first substrate 102 onwhich the nonlinear resistance elements are formed and a secondsubstrate 109 (refer to FIG. 29) having opposite electrodes 110 (asindicated by phantom lines in FIG. 30) formed in such a way as to facethe display electrodes 106 formed on the first substrate 102.

After applying liquid crystal-molecular alignment treatment to thesurfaces of the first substrate 102 and the second substrate 109, thetwo substrates are bonded together with a sealing portion 108 such thatthe surfaces of the both substrates face each other at a predeterminedspacing, and liquid crystals are sealed in a gap formed therebetween,thus forming a liquid crystal display. A region surrounded by a phantomline 118 as indicated in FIG. 29 and a solid line 118 as indicated inFIG. 30 represents a display region of the liquid crystal display.

However, the liquid crystal display having the conventional nonlinearresistance elements described above poses a problem of an after-imagephenomenon occurring when an image displayed is changed in the course ofdriving the liquid crystal display.

Referring to FIG. 33, the after-image phenomenon is described. Herein,the liquid crystal display is assumed to display images in “normallywhite” mode.

FIG. 33 indicates variation in transmissivity of light when an appliedvoltage for a random pixel is varied for every 5 minutes . Specifically,a voltage (VI) for providing a display of 50% transmissivity is appliedfor first 5 minutes (unselect period: T1), then a voltage (V2) forproviding a display of 10% transmissivity is applied for another 5minutes (select period: T2), and further a voltage (V3) at the samelevel as that of the voltage (V1) applied for the first unselect periodT1 is applied for yet another 5 minutes (unselect period: T3).

The after-image phenomenon is a phenomenon wherein a difference (ΔT) intransmissivity between the unselect period T1 and the unselect period T3develops although the voltages applied for respective periods are equal.With the liquid crystal display described above, the difference ΔT intransmissivity was found to be 5%.

The occurrence of the after-image phenomenon results in the display ofan image with its contents different from those of an originallyintended image.

Therefore, an image sticking phenomenon, that is, the after-imagephenomenon degrades considerably the quality of images displayed by theliquid crystal display, posing a serious problem in commercialapplication thereof.

A primary cause for the occurrence of the after-image phenomenon is ad-c voltage component of a voltage applied on the liquid crystal layerwhen driving the liquid crystal display. Owing to the d-c voltagecomponent, a polarization phenomenon of alignment layers used foraligning liquid crystal molecules in a predetermined direction and thedegradation of liquid crystals themselves occurs, resulting in theoccurrence of the after-image phenomenon.

FIG. 34 is a graph showing a current-voltage characteristic (I-Vcharacteristic) of a non-linear resistance element composed of a“tantalum film-tantalum oxide film-indium tin oxide film” structureaccording to a conventional structure.

As shown in the figure, variation in current value differs considerablydepending on the polarity of an applied voltage, demonstrating anasymmetrical current-voltage characteristic with respect to a voltage atzero.

As a means for achieving an improvement on the asymmetricalcurrent-voltage characteristic, it is conceivable to replace the indiumtin oxide film composing the upper electrode 105 of nonlinear resistanceelements with such a metal film as a chromium (Cr) film, a titanium (Ti)film or the like.

Such replacement of the indium tin oxide film with the chromium film orthe titanium film in forming the upper electrode 105 can moderate tosome extent the asymmetry of the current-voltage characteristic as shownin FIG. 34, but is still far from achieving a fully symmetricalcurrent-voltage characteristic.

Further, an offset driving method is proposed to prevent the d-c voltagecomponent from being applied on the liquid crystal layer through thenonlinear resistance elements having the asymmetrical current-voltagecharacteristic. The offset driving method is described hereafter withreference to FIG. 35.

As shown in FIG. 35, the offset driving method is a method of drivingthe liquid crystal display by varying voltages applied in a selectperiod (Ts) and a hold period (Th), respectively, depending on thepolarity of an electric field, that is, a (+) field or a (−) field sothat the d-c voltage component will not be applied on the liquid crystallayer by compensating for the asymmetric characteristic of the elementwith a varying driving voltage.

Voltages applied in the select period (Ts) are denoted Va1 and Va2, andvoltages applied in the hold period (Th) are Vb1 and Vb2.

With the offset driving method as shown in FIG. 35, the d-c voltagecomponent of a voltage applied between the display electrodes 106 andthe opposite electrodes 110, disposed facing each other, with the liquidcrystal layer sandwiched therebetween can be reduced.

However, asymmetrical voltages, for example, Vb2 and Vb1 are applied onthe signal electrodes 107 as shown in FIGS. 30 and 31, but symmetricalvoltages are applied on the liquid crystal layer. Consequently, avoltage between the signal electrodes 107 on the first substrate 102composing the MIM elements and the display electrodes 106 contains thed-c voltage component. Furthermore, the d-c voltage component occurssimilarly between the opposite electrodes 110 and the signal electrodes107.

As a result, with nonlinear resistance elements having the asymmetriccurrent-voltage characteristic, it was impossible to reduce sufficientlythe d-c voltage component impressed on the liquid crystal layer,eliminating the after-image phenomenon completely.

Therefore, it is an object of the present invention to provide an liquidcrystal display capable of displaying images of excellent qualitywithout the effect of the after-image phenomenon by reducing a d-cvoltage component impressed on the liquid crystal layer in its nonlinearresistance elements having an asymmetrical current-voltagecharacteristic.

DISCLOSURE OF THE INVENTION

To achieve the aforesaid object, the present invention provides a methodof manufacturing liquid crystal display and a liquid crystal device asfollows.

According to the present invention, a method of manufacturing the liquidcrystal display comprises the following steps:

A. a process of forming a metal film on a substrate, then forming aplurality of anodic oxidation electrodes, a common electrode connectingtogether the anodic oxidation electrodes, lower electrodes of nonlinearresistance elements, and connection portions connecting the lowerelectrodes with the anodic oxidation electrodes by patterning on themetal film by means of a photo etching method;

B. a process of forming an insulation film by means of an anodicoxidation method applied to each of the anodic oxidation electrodes, theconnection portions, and the lower electrodes, joined integrally withthe common electrode, using the common electrode as an anode;

C. a process of forming a transparent and electrically conductive filmon the insulation film and the substrate, then forming displayelectrodes on the substrate such that each of the display electrodes isprovided with an overlapping portion covering a part of each of theconnection portions, and forming a signal electrode on each of theanodic oxidation electrodes such that a gap is provided between each ofthe signal electrodes and each of the lower electrodes, then forming afirst upper electrode connected with each of the single electrodes and asecond upper electrode connected with each of the display electrodes, oneach of the lower electrodes by patterning on the transparent andelectrically conductive film by means of the photo etching method;

D. a process of forming a photosensitive resin in a region covering eachof the lower electrodes, the first and the second upper electrodes; and

E. a process of etching the metal film and each of the connectionportions, having a structure of laminated layers composed of the metalfilm and the insulation film of the anodic oxidation film formed on themetal film, completely down to the surface of the substrate by means ofthe etching method using the photosensitive resin, the displayelectrodes, and the signal electrodes as etching masks such that each ofthe connection portions automatically matches a plurality of sides ofthe display electrodes and the signal electrodes, separating the anodicoxidation electrodes disposed underneath the signal electrodes,overlapping portions of each of the connecting portions, disposedunderneath each of the display electrodes, and the lower electrodes fromeach other such that each of the lower electrodes is isolated and formedin a shape resembling an island, forming a first nonlinear resistanceelement and a second nonlinear resistance element composed of each ofthe lower electrodes, the insulation film and the first and second upperelectrodes, respectively, and electrically isolating the anodicoxidation electrodes form each other by removing the common electrodeconnecting the plurality of the anodic oxidation electrodes with eachother by means of the etching method using the signal electrodes asetching masks.

In the step C, the display electrodes are formed such that each of thedisplay electrodes is provided with overlapping portions covering partsof each of the connecting portions connecting the lower electrode of thenonlinear resistance element for a pixel adjacent to the relevant pixelwith the anodic oxidation electrode.

The steps C, D, and E described as above may be replaced with thefollowing steps:

a process of forming a metal film on the insulation film and thesubstrate which were formed in step B, then forming signal electrodes onthe anodic oxidation electrodes, and forming a first upper electrodeconnected with each of the signal electrodes and a second upperelectrode having a paid on each of the lower electrodes by patterning onthe metal film by mans of the photo-etching method;

a process of forming a transparent and electrically conductive film onthe insulation film and the substrate including the pad surface, thenforming display electrodes electrically isolated from the signalelectrodes and the lower electrodes such that each of the displayelectrodes is provided with an overlapping portion covering a part ofeach of the connection portions and the pad by patterning on thetransparent and electrically conductive film by the photo-etchingmethod;

a process of forming a photosensitive resin in a region covering each ofthe lower electrodes, the first and the second upper electrodes; and

a process of etching the metal film and each of the connection portions,having a structure of laminated layers composed of the metal film andthe insulating film of the anodic oxidation film formed on the metalfilm, completely down to the surface of the substrate by means of theetching method using the photosensitive resin, the display electrodes,and the signal electrodes, each made of different material, as etchingmasks such that each of the connection portions automatically matches aplurality of sides of the display electrodes and the signal electrodes,separating the anodic oxidation electrodes disposed underneath thesignal electrodes, overlapping portions of each of the connectionportions, disposed underneath each of the display electrodes, and thelower electrodes from each other such that each of the lower electrodesis isolated and formed in a shape resembling an island, forming a firstnonlinear resistance element and a second nonlinear resistance elementcomposed of each of the lower electrodes, the insulation film and thefirst and second upper electrodes, respectively, and electricallyisolating the anodic oxidation electrodes from each other by removingthe common electrode connecting the plurality of the anodic oxidationelectrodes with each other by means of the etching method using thesignal electrodes as etching masks.

The process of forming a photosensitive resin, i a region covering eachof the lower electrodes and the first and second upper electrodes, andthe following process thereto may be replaced with the following steps:

a process of forming a photosensitive resin in a region covering abouthalf of the first upper electrode and the second upper electrode,respectively, on the side facing each other, on each of the lowerelectrodes, and the surface of each of the lower electrodestherebetween; and

a process of etching each of the connection portions, having a structureof laminated layers composed of the metal film and the insulation filmof the anodic oxidation film formed on the metal film, and each of thelower electrodes completely down to the surface of the substrate bymeans of the etching method using the photosensitive resin, the displayelectrodes, the first upper electrode, the second upper electrode, andthe signal electrodes, all of which are made of different materials, asetching masks such that each of the connection portions automaticallymatches with a plurality of sides of the display electrodes and thesignal electrodes, separating the anodic oxidation electrodes disposedunderneath the signal electrodes, overlapping portions of each of theconnection portions disposed underneath each of the display electrodes,and the lower electrodes from each other such that each of the lowerelectrodes automatically matches an external side of the first upperelectrode and the second upper electrode, respectively, forming a firstnonlinear resistance element and a second nonlinear resistance elementcomposed of each of the lower electrodes, the insulation film and thefirst and second upper electrodes, respectively, and electricallyisolating the anodic oxidation electrodes from each other by removingthe common electrode connecting the plurality of the anodic oxidationelectrodes with each other by means of the etching method using thesignal electrodes as etching masks.

In the steps of the method of manufacturing the liquid crystal display,forming a metal film on the substrate, and forming a plurality of anodicoxidation electrodes, a common electrode connecting together the anodicoxidation electrodes, lower electrodes of nonlinear resistance elements,and connection portions connecting each of the lower electrodes witheach of the anodic oxidation electrodes by patterning on the metal filmby means of the photo-etching method,

each of the connection portions is formed integrally with the anodicoxidation electrode formed under the signal electrode in a row or columndifferent from that for a signal electrode connected with the nonlinearresistance element for the relevant pixel; and

in the step of forming the display electrodes, the display electrodesare formed such that each of the display electrodes is provided withoverlapping portions covering parts of each of the connection portions,connected with the lower electrode of the nonlinear resistance elementfor a pixel adjacent to the relevant pixel.

In the steps A to E of the method of manufacturing the liquid crystaldisplay, the steps D and E may e replaced with the following steps:

a process of forming an overcoating insulation film on the entiresurface of the substrate, after steps A to C, including the surfaces ofall the electrodes and the connection portions formed thereon, after theaforesaid processes, and forming openings by the photo etching method inthe overcoating insulation film in regions covering the overlappingportions where the display electrodes are partially overlapped with theconnection portions, and parts of the connection portions, in regionsprotruding from the display electrodes; and

a process of etching each of the connection portions, having a structureof laminated layers composed of the metal film and the insulation filmof the anodic oxidation film formed on the metal film, completely downto the surface of the substrate by means of the etching method using theovercoating insulation film, the display electrode inside the opening inthe overcoating insulation film and the signal electrode as etchingmasks such that each of the connection portions automatically matcheswith a plurality of sides of the display electrode and the signalelectrode, separating the anodic oxidation electrode disposed underneaththe signal electrode, overlapping portions of each of the connectionportions disposed underneath each of the display electrodes, and thelower electrodes form each other such that each of the lower electrodesis isolated and formed in an island-like shape, and forming a firstnonlinear resistance element and a second nonlinear resistance elementcomposed of the aforesaid lower electrode, the insulation film and thesecond upper electrodes, respectively.

By the method described above, it is possible to manufacture efficientlya liquid crystal display, having a pair of nonlinear resistance elementsin good symmetry per pixel and having excellent quality of image withoutthe effect of the after-image phenomenon.

In addition, the present invention provides another liquid crystaldisplay described hereinafter.

The liquid crystal display provided with display electrodes disposed ina matrix configuration on a substrate, each of the display electrodesconstituting a pixel, has the following constitution.

The liquid crystal display comprises an anodic oxidation electrode andlower electrodes each resembling an island in shape, both of which arecomposed of a metal film and formed on a substrate, an insulation filmformed on the metal film, two upper electrodes composed of a transparentand electrically conductive film formed on each of the lower electrodeswith the insulation film interposed in-between, display electrodescomposed of a transparent and electrically conductive film, and signalelectrodes composed of a metal film or a metal film and a transparentand electrically conductive film.

The two upper electrodes so disposed as to cross the lower electrode,the insulation film, and the lower electrode constitute two nonlinearresistance elements. One of the two upper electrodes, constituting oneof the nonlinear resistance elements, is connected with one of thesignal electrodes while the other is connected with one of the displayelectrodes.

The display electrodes constituting the pixels consist of two types ofdisplay electrodes, one type provided thereunder with an overlappingportion having a remaining double layer film, consisting of the samemetal film as that for the lower electrodes and the insulation film, andthe other type not provided thereunder with the overlapping portion.

In the case of a liquid crystal display wherein a plurality of displayelectrodes constitute one pixel, the display electrodes for the pixelconsist of one display electrode provided thereunder with overlappingportions having a remaining double layer film, consisting of the samemetal film as that for the lower electrodes and the insulation film, andthe other display electrode not provided thereunder with the overlappingportion.

Or preferably, the display electrodes for constituting one pixel mayconsist of one display electrode provided thereunder with theoverlapping portion having a remaining double layer film, consisting ofthe same metal film as that for the lower electrodes and the insulationfilm, and the other display electrode not provided thereunder with theoverlapping portion, and furthermore, the nonlinear resistance elementsof a plurality of display electrodes for constituting one pixel may bedisposed to converge around a focal point.

Also, the present invention provides a liquid crystal display comprisingan anodic oxidation electrode and lower electrodes, both of which arecomposed of a metal film and formed on a substrate, an insulation filmformed on the surface of the metal film, upper electrodes formed on eachof the lower electrodes with the insulation film interposed in-between,display electrodes connected with the upper electrodes, and signalelectrodes composed of the lower electrode or the lower electrode andthe insulation film.

And the upper electrodes so disposed as to cross the lower electrode,the insulation film, and the lower electrode constitute nonlinearresistance elements, and the anodic oxidation electrode or the anodicoxidation electrode and part of the insulation film are provided withoverlapping portions kept intact under each of the display electrodes.

It is desirable that one of the two upper electrodes, constituting oneof the nonlinear resistance elements, is connected with one of thesignal electrodes while the other is connected with one of the displayelectrodes.

It is important to reduce an area ratio of the peripheral region of thedisplay electrodes, not utilized for displaying images, to the displayelectrodes thereof to improve the quality of images. Also, in the caseof a high density liquid crystal display, it is important to minimizethe area of the peripheral region thereof.

For this reason, the display electrodes having the double layer filmsconsisting of the metal film and the insulation film thereunder and thedisplay electrodes not having the same can be provided by concentratingthe nonlinear resistance elements, resulting in reduction of the areaoccupied by the connection portions. The connection portions being theareas shielding light, brighter display can be obtained in this way.

Furthermore, in the case of a liquid crystal display wherein a pluralityof display electrodes constitute one pixel, the display electrodes canbe made best use of by providing fewer number of the display electrodeshaving the double layer film thereunder than that of the displayelectrodes not having the same by concentrating the nonlinear resistanceelements because the area of the connection portions shielding light isthus reduced.

In the case of a high density liquid crystal display provided withpixels at a small pitch or a large-sized liquid crystal display, theanodic oxidation electrode has limitations in its width. Accordingly,the anodic oxidation electrode with a large width is used until theanodic oxidation process is completed, and then a part thereof isremoved after the display electrodes are formed. As this will enable theanodic oxidation electrode to have a large width, the insulation filmrequired in the high density liquid crystal display or the large-sizedliquid crystal display can be formed uniformly in a short time.

Furthermore, by using a part of the anodic oxidation electrode and thedisplay electrode as etching masks when splitting the connection portionbetween the anodic oxidation electrode and the lower electroderesembling an island in shape, the insulation film can be formeduniformly in a short time without increasing the number of processingsteps.

Also, the overlapping portions of the anodic oxidation electrode,remaining intact under the display electrodes, can then be used for apart of black matrices, contributing to an improvement on accuracy inaligning the black matrices with the display electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a portion of a liquid crystal display,constituting nonlinear resistance elements, according to a firstembodiment of the invention,

FIG. 2 an expanded sectional view taken along the line II—II of FIG. 1,

FIG. 3 a diagram showing a current-voltage characteristic of thenonlinear resistance elements,

FIG. 4 a diagram showing an after-image phenomenon in the liquid crystaldisplay, and

FIG. 5 a timing chart showing a driving waveform applied on scanningelectrodes of the liquid crystal display.

FIG. 6 is a plan view illustrating an initial step of a method ofmanufacturing the liquid crystal display according to the firstembodiment of the invention,

FIGS. 7 and 8 are plan views illustrating intermediate steps of thesame, and

FIG. 9 a plan view showing completion of a final step of the same.

FIG. 10 is a plan view showing an initial step of processing forillustrating a liquid crystal display according to a second embodimentof the invention, and a method of manufacturing the same.

FIGS. 11 to 14 are plan views respectively illustrating intermediate andfinal steps of the same, and

FIG. 15 is an expanded sectional view taken along the line XV—XV of FIG.14.

FIGS. 16 and 17 are plan views respectively showing intermediate andfinal steps for illustrating a liquid crystal display according to athird embodiment of the invention, and a method of manufacturing thesame.

FIGS. 18 to 19 are plan views respectively showing intermediate andfinal steps for illustrating a liquid crystal display according to afourth embodiment of the invention, and a method of manufacturing thesame and

FIG. 20 is an expanded sectional view taken along the line XX—XX of FIG.19.

FIGS. 21 and 22 are plan views of a portion of a liquid crystal displayaccording to a variation of the embodiments of the invention,constituting nonlinear resistance elements thereof.

FIG. 23 is a plan view of a portion constituting nonlinear resistanceelements of a liquid crystal display according to a fifth embodiment ofthe invention, and

FIG. 24 a sectional view taken along the line XXIX—XXIX of FIG. 23.

FIG. 25 is a plan view of a portion constituting nonlinear resistanceelements of a liquid crystal display according to a sixth embodiment ofthe invention, and

FIG. 26 a sectional view taken along the line XXVI—XXVI of FIG. 25.

FIG. 27 is a plan view of a portion constituting nonlinear resistanceelements of a liquid crystal display according to a seventh embodimentof the invention, and

FIG. 28 a sectional view taken along the line XXVIII—XXVIII of FIG. 27.

FIG. 29 is a plan view showing a conventional liquid crystal display ofa similar type,

FIG. 30 an enlarged plan view showing a region inside a circle denotedby A as indicated by a dash and double dotted line in FIG. 29,

FIG. 31 a plan view showing a nonlinear resistance element, and

FIG. 32 a sectional view taken along the line B—B of FIG. 31

FIG. 33 is a diagram showing an after-image phenomenon in theconventional liquid crystal display,

FIG. 34 a diagram showing a current-voltage characteristic of thenonlinear resistance element of the same, and

FIG. 35 a timing chart showing a waveform of a driving voltage appliedon signal electrodes of the same.

BEST MODE FOR CARRYING OUT THE INVENTION

This invention will be described in further detail hereinafter withreference to the accompanying drawings.

First Embodiment

FIG. 1 is a plan view showing a portion of a region for a firstsubstrate for forming nonlinear resistance elements (MIM elements) of aliquid crystal display according to a first embodiment of the invention.FIG. 2 is an expanded sectional view taken along the line II—II of FIG.1. Firstly, referring to these figures, the constitution of the liquidcrystal display according to the first embodiment of the invention isdescribed.

An anodic oxidation electrode 3, lower electrodes 2, and connectionportions 4 for connecting the anodic oxidation electrode 3 with thelower electrodes 2, all of which are composed of a metal film, that is,a tantalum (Ta) film, are provided on a transparent first substrate 1,that is, an active substrate for composing the nonlinear resistanceelements.

One end of the anodic oxidation electrode 3 is connected with a commonelectrode 6, and the other end with an input terminal 7 for applyingsignals from an external circuit to the nonlinear resistance elements.The common electrode 6 is used as an electrode for the anodic oxidationprocess whereby an insulation film 8 is formed on the surface of thelower electrode 2.

In FIG. 1, a region indicated by a dash and double-dotted line 5 of oneof the connection portions 4, between a signal electrode 9 and one ofdisplay electrodes 12, the same region of another of the connectionportions 4, between the common electrode 6 and another of the displayelectrodes 12, disposed in a region on the right side of a first upperelectrode 10, and the like will be removed in a step of a manufacturingmethod described hereafter.

This means that FIG. 1 shows merely an intermediate step of amanufacturing process for clarity in description.

An insulation film 8 composed of a tantalum oxide (Ta₂O₅) film formed bythe anodic oxidation of the lower electrodes 2 is provided on thesurface of the lower electrodes 2.

Then a transparent and electrically conductive film is formed on theanodic oxidation electrode 3, serving as the signal electrode 9. A firstupper electrode 10 connected with the signal electrode 9 is provided onone of the lower electrodes 2, and further a second upper electrode 11connected with one of the display electrodes 12 is provided on theaforesaid lower electrode 2.

The first upper electrode 10 and the second upper electrode 11 areformed on each of the lower electrodes 2, resembling an island in shape,with the insulation film 8 interposed in-between.

The lower electrode 2, the insulation film 8, and the first upperelectrode 10 constitute a first nonlinear resistance element 13 whilethe lower electrode 2, the insulation film 8, and the second upperelectrode 11 constitute a second nonlinear resistance element 14.

Herein, the signal electrode 9. the first upper electrode 10, the secondupper electrode 11, and the display electrodes 12 are all composed of atransparent and electrically conductive film, for example, an indium tinoxide (ITO) film.

The signal electrode 9 for connection with the external circuit isfurther connected with the input terminal 7.

A region for each of the display electrodes 12 has an overlappingportion 15 partially overlapped with a portion of a region for each ofthe connection portions 4 connecting the anodic oxidation electrode 3with each of the lower electrodes 2.

The display electrodes 12 are separated from the signal electrode 9 in apart of the region for each of the connection portions 4, thus formingthe lower electrodes 2 each resembling an island in shape.

Herein, the first nonlinear resistance element 13 and the secondnonlinear resistance element 14, provided in a region between the signalelectrode 9 and the display electrodes 12, are composed of “an indiumtin oxide film—a tantalum oxide film—a tantalum film” and “a tantalumfilm—a tantalum oxide film—an indium tin oxide film”, connected in thisorder, respectively.

This means that an electric current path is provided between the signalelectrode 9 and each of the display electrodes 12 such that electriccurrent flows from “the indium tin oxide film—the tantalum oxidefilm—the tantalum film” of the first nonlinear resistance element 13 to“the tantalum film—the tantalum oxide film—the indium tin oxide film” ofthe second nonlinear resistance element 14.

As a result, connection from the signal electrode 9 to each of thedisplay electrodes 12 at one of the nonlinear resistance elements, andconnection from the aforesaid display electrode 12 to the signalelectrode 9 at the other of the nonlinear resistance elements becomestructurally symmetrical to each other.

The current-voltage (I-V) characteristic of the nonlinear resistanceelements according to the first embodiment of the invention is describedhereafter with reference to FIG. 3.

As shown in FIG. 3, the nonlinear resistance elements having symmetricalconnections between the display electrodes and the signal electrode showa characteristic of symmetrical current (I) curves with respect to thevoltage (V) axis.

Now, referring to FIG. 4, an after-image phenomenon occurring in thiscase is described hereafter.

Similarly to FIG. 33 illustrating the after-image phenomenon occurringwhen driving the conventional liquid crystal display, FIG. 4 showsvariation in transmissivity when an applied voltage is varied every 5minutes with respect to a pixel of the liquid crystal display providedwith the nonlinear resistance elements according to the invention. Thisliquid crystal display is driven in normally white mode.

Firstly, a voltage (V1) for display at 50% transmissivity is applied for5 minutes (unselect period: T1), then a voltage (V2) for display at 10%transmissivity is applied for another 5 minutes (select period: T2), andfurther, a voltage (V3) at the same level as that of the voltage (V1)applied for the initial unselect period T1 is applied for yet another 5minutes (unselect period: T3).

The after-image phenomenon is a phenomenon wherein a difference (ΔT) intransmissivity occurs between the unselect period T1 and the otherunselect period T3 although the applied voltages for the respectiveperiods are equal.

With use of the nonlinear resistance elements according to the firstembodiment of the invention, the difference (ΔT) in transmissivity isreduced down to 1% or less as shown in FIG. 4. Furthermore, with theelapse of time, the difference ΔT in transmissivity declines rapidly.

Referring to FIG. 5, an example of the waveform of a voltage applied tothe signal electrode 9 of the liquid crystal display is describedhereafter.

Voltages applied in a select period Ts and a hold period Th are denotedVs1 and Vh1, respectively, in a (+) electric field, and Vs2 and Vh2,respectively, in a (−) electric field. Since the nonlinear resistanceelements have a symmetrical current-voltage characteristic, the absolutevalue of the voltage Vs1 can be made equal to that of the voltage Vs2,and also the absolute value of the voltage Vh1 equal to that of thevoltage Vh2.

As is evident from the foregoing description, the nonlinear resistanceelements of the liquid crystal display constituted according to thisembodiment of the invention obtain the symmetrical current-voltagecharacteristic.

Consequently, a d-c voltage component of a voltage applied to a liquidcrystal layer during driving can be nearly eliminated and the waveformof a voltage applied to the signal electrode can be made symmetrical.

As a result, the d-c voltage component applied between the signalelectrode and the display electrodes as well as between the signalelectrode and the opposite electrodes disappears, and the occurrence ofthe after-image phenomenon posing a problem with displaying images canbe prevented. Thus the liquid crystal display capable of displayingimages of excellent quality is obtained.

Now a method of manufacturing the active substrate of the liquid crystaldisplay as shown in FIGS. 1 and 2 is described with reference to FIGS. 6to 9. FIGS. 6 to 9 are plan views illustrating steps in sequence of themethod of manufacturing the active substrate of the liquid crystaldisplay according to the first embodiment of the invention.

Firstly, as shown in FIG. 6, a metal film made of tantalum (Ta) isformed to a thickness of 250 nm on the entire surface of the firstsubstrate 1, which is the active substrate made of glass, by thesputtering method.

Then, a photosensitive resin (not shown) is formed on the entire surfaceof the tantalum film using a roll coater, a pattern is formed on thephotosensitive resin by photolithographic techniques using apredetermined photo mask, and using the patterned photosensitive resinas an etching mask, the tantalum film is etched by the photo-etchingmethod, forming the lower electrodes 2, the anodic oxidation electrode 3connected with the lower electrodes 2 via the connection portions 4, andthe common electrode 6 connected with the anodic oxidation electrode 3.

Herein the etching of the tantalum film is carried out by use of thereactive ion etching system (hereinafter referred to as “RIE”).

The etching is carried out using a mixture of sulfur hexafluoride (SF₆)gas and oxygen (O₂) gas under a condition of SF₆ flow rate at 100˜200sccm, O₂ flow rate at 10˜40 sccm, and pressure at 4˜12×10⁻² torr withpower consumption of 0.2˜0.5 kW/cm².

Thereafter, the anodic oxidation method is applied to the tantalum filmusing the common electrode 6 as an anode, and an aqueous solutioncontaining 0.01˜1.0 wt % of citric acid or ammonium borate as an anodicoxidation electrolyte and by applying a voltage at 10-20V.

Thereupon, the insulation film composed of a tantalum oxide (Ta₂O₅) filmis formed to a thickness of 35 nm on the lower electrodes 2, the anodicoxidation electrode 3, and the surfaces of the sidewall and topwall ofthe connection portions 4.

Then, as shown in FIG. 7, the indium tin oxide (ITO) film as atransparent and electrically conductive film is formed to a thickness of100 nm on the entire surface of the first substrate 1 by use of thesputtering system. Thereafter, a photosensitive resin is formed on theindium tin oxide film.

In the next step, by etching the indium tin oxide film, a pattern isformed simultaneously for the display electrodes 12, the second upperelectrode 11 connected with one of the display electrodes 12, the signalelectrode 9, the first upper electrode 10 connected with the signalelectrode 9, and the input terminal 7 connected with the signalelectrode 9.

Hereupon, a patterning on the indium tin oxide film is formed such thatthe input terminal 7 is completely covered with the indium tin oxidefilm and extended to the left side in FIG. 7, and the tantalum film onthe common electrode 6 is exposed.

The etching of the indium tin oxide film is carried out by use of thewet etching system using an aqueous solution of ferric oxide andhydrochloric acid as an etchant at a temperature set in the range of30˜40° C.

As shown in the plan view of FIG. 7, parts of regions for the displayelectrodes 12 cover parts of a region for each of the connectionportions 4. Regions where the display electrodes 12 are partiallyoverlapped with the connection portions 4 are denoted as overlappingportions 15.

Then as shown in FIG. 8, photosensitive resin is applied to the entiresurface and a photosensitive resin 21 covering the first upper electrode10 and the second upper electrode 11 is formed by the photolithographictechniques using a predetermined photo mask.

And the etching of the connection portion 4 connecting the anodicoxidation electrode 3 with the common electrode 6 and also theconnection portion 4 connecting the lower electrode 2 with the displayelectrodes 12, in regions protruding from the display electrodes 12, iscarried out by use of the RIE system using the display electrodes 12 andthe photosensitive resin 21 as etching masks.

The etching is carried out using a mixture of sulfur hexafluoride (SF₆)gas and oxygen (O₂) gas under a condition of SF₆ flow rate at 100˜200sccm, O₂ flow rate at 10˜40 sccm, and pressure at 4˜12×10⁻² torr withpower consumption of 0.2˜0.5 kW/cm².

Under the etching condition described above, only the tantalum film ofthe connection portions 4 and the tantalum oxide film of the insulationfilm 8 are removed, hardly etching the indium tin oxide film.

As shown in FIG. 9, by the etching process described above, theconnection portions 4 between the anodic oxidation electrode 3 and thedisplay electrodes 12 are split, separating the former from the latter,the common electrode 6 is. removed, and the connection portions 4between the display electrodes 12 and the lower electrodes 2 are split,separating the former from the latter.

As shown in FIGS. 9 and 2, by steps of processing described in theforegoing, the first nonlinear resistance element 13 comprising each ofthe lower electrodes 2, resembling an island in shape and separated fromthe anodic oxidation electrode 3, the insulation film 8 formed on theaforesaid lower electrode 2, and the first upper electrode 10 connectedwith the signal electrode 9 is formed.

Further, the second nonlinear resistance element 14 comprising each ofthe lower electrodes 2, resembling an island in shape, the insulationfilm 8 formed on the aforesaid lower electrode 2, and the second upperelectrode 11 is formed.

Then, the signal electrode 9 is formed such that one end thereof isconnected with the input terminal 7.

Driving signals applied from the external circuit are impressed on thedisplay electrodes 12 through a route of “the input terminal 7—thesignal electrode 9—the first nonlinear resistance element 13—the secondnonlinear resistance element 14”.

Each of the display electrodes 12 is provided with an overlappingportion 15 partially overlapping with each of the connection portions 4composed of the tantalum film and substantially resembling the letter Lin shape.

In this manufacturing method, the connection portions 4 are processed bythe etching system using the photosensitive resin 21 and the displayelectrodes 12 as etching masks so that the connection portions 4 can beformed so as to match the underside region for the display electrodes12.

Since the etching process is applied using the photosensitive resin 21formed so as to cover the first upper electrode 10 and the second upperelectrode 11 as an etching mask, the lower electrodes 2 each resemblingan island in shape can be formed.

Herein, the first nonlinear resistance element 13 and the secondnonlinear resistance element 14, provided in a region between the signalelectrode 9 and the display electrodes 12, comprise “an indium tin oxidefilm—a tantalum oxide film—a tantalum film” structure and “a tantalumfilm—a tantalum oxide film—an indium tin oxide film” structure,respectively.

This means that an electric current path is provided between the signalelectrode 9 and each of the display electrodes 12 such that electriccurrent flows from “the indium tin oxide film—the tantalum oxidefilm—the tantalum film” of the first nonlinear resistance element 13 to“the tantalum film—the tantalum oxide film—the indium tin oxide film” ofthe second nonlinear resistance element 14.

As a result, connection from the signal electrode 9 to each of thedisplay electrodes 12 at one of the nonlinear resistance elements, andconnection from the aforesaid display electrode 12 to the signalelectrode 9 at the other of the nonlinear resistance elements becomestructurally symmetrical to each other.

By adoption of the method of manufacturing the active substrate,described in the first embodiment of the invention, the nonlinearresistance elements having an excellent symmetrical characteristic canbe manufactured.

As a result, the d-c voltage component applied to a liquid crystal layerdisappears and the occurrence of the after-image phenomenon posing aproblem with displaying images can be prevented while the displayelectrodes can be utilized as an etching mask.

Accordingly, in a step of separating the anodic oxidation electrode 3from the lower electrodes 2, it is sufficient only to form thephotosensitive resin 21 on the upper surfaces of the first nonlinearresistance element 13 and the second nonlinear resistance element 14.

As a result, it has become possible to relax requirement for accuracy inpositioning a region for the photosensitive resin 21 from that in thepast. Furthermore, separation of the connection portions 4 from thelower electrodes 2 as well as from the anodic oxidation electrode 3 isensured. Thus the liquid crystal display capable of displaying images ofexcellent quality is obtained.

Second Embodiment

Referring to FIGS. 10 to 15, the structure of a first substrate forforming thereon nonlinear resistance elements of a liquid crystaldisplay according to a second embodiment of the invention and the methodof manufacturing the same are described hereafter.

FIGS. 10 to 14 are plan views showing steps of manufacturing the liquidcrystal display according to the second embodiment of the invention andFIG. 15 is an expanded view taken along the line XV—XV in FIG. 14.

Firstly, the constitution of the liquid crystal display according to thesecond embodiment is described with reference to FIGS. 14 and 15.

A nonlinear resistance element portion provided between the signalelectrode 35 and the display electrodes 51 comprises a first nonlinearresistance element 62 composed of a first upper electrode 36 made of achromium film, an insulation film 60 made of a tantalum oxide film, anda lower electrode 32 made of a tantalum film.

Also the nonlinear resistance element portion comprises a secondnonlinear resistance element 63 composed of the lower electrode 32 madeof the tantalum film, the insulation film 60 made of the tantalum oxidefilm, and a second upper electrode 38 made of the chromium film.

One end of respectively anodic oxidation electrodes 29 and 30 isconnected with a common electrode, and the other end thereof with inputterminals 40.

The insulation film 60 made of the tantalum oxide film formed byprocessing the lower electrodes 32 by the anodic oxidation method isprovided on the surface of the lower electrodes 32.

Further, a chromium film as a metal film is formed on the upper surfaceof respectively the anodic oxidation electrodes 29 and 30 constitutingsignal electrodes 35 composed of a double layer film made of thetantalum film and the chromium film.

Each of the signal electrodes 35 is provided with an extended portioncrossing each of the lower electrodes 32 and serving as the first upperelectrode 36 provided on the aforesaid lower electrode 32.

The second upper electrode 38 crossing the aforesaid lower electrode 32and disposed thereon is connected with each of the display electrodes 51via a pad 37. The second upper electrode 38 is composed of the chromiumfilm. The display electrodes 51 are composed of a transparent andelectrically conductive film such as an indium tin oxide film.

As shown in FIGS. 12 and 13, connection portions 31 connecting the lowerelectrodes 32 with the anodic oxidation electrode 29 are provided withoverlapping portions 53 where the display electrodes 51 are partiallyoverlapped with the connection portions 31. The insulation film 60 isinterposed between the display electrodes 51 and the connection portions31.

Each of the overlapping portions 53 has a width about half as wide asthe width of each of the connection portions 31, and a part of theconnection portion 31, protruding from the region of the displayelectrode 51, is denoted as an exposed region 57.

As shown in FIG. 14, the lower electrodes 32 each resembling an islandin shape are separated from the anodic oxidation electrode 29 byremoving the exposed region 57 after the display electrodes 51 areformed.

Further, in each of the input terminals 40, an input electrode 39 madeof an chromium film, and an input electrode 54 for connection, made of atransparent and electrically conductive film, are provided.

Consequently, the first nonlinear resistance element 62 provided betweenthe signal electrode 35 and each of the display electrodes 51 has astructure consisting of “chromium film—tantalum oxide film—tantalumfilm” while the second nonlinear resistance element 63 has a structureconsisting of “tantalum film—tantalum oxide film—chromium film”.

As a result, connection from the signal electrode 35 to each of thedisplay electrodes 51 at one of the nonlinear resistance elements, andconnection from the aforesaid display electrode 51 to the signalelectrode 35 at the other of the nonlinear resistance elements becomessymmetrical to each other in structure.

Accordingly, the nonlinear resistance element portion having anexcellent symmetrical characteristic is obtained, eliminating thereby ad-c voltage component impressed on a liquid crystal layer. Thus theoccurrence of the after-image phenomenon posing a problem with the imagequality of display can be prevented.

Referring to FIGS. 14 and 15, the method of manufacturing the liquidcrystal display according to the second embodiment is described indetail hereafter.

As shown in FIG. 10, a tantalum (Ta) film as a metal film is formed to athickness of 100 nm on a first substrate 1 made of glass by use of thesputtering system. Thereafter a photosensitive resin (not shown) isformed on the tantalum film.

Then by means of an etching process using the photosensitive resin filmas an etching mask, patterns are formed for the lower electrodes 32, theanodic oxidation electrode 29 connected with one of the lower electrodes32 via the connection portion 31, the common electrode 34 connected withthe anodic oxidation electrodes 29 and 30, and the input terminals 40for inputting scanning signals sent out from the external circuit, allof which are composed of the tantalum film. The etching of the tantalumfilm is carried out by use of the RIE system under the etching conditiondescribed in the foregoing.

FIG. 10 shows the anodic oxidation electrode 30 corresponding a n-thscanning electrode and the anodic oxidation electrode 29 correspondingto a (n+1)th scanning electrode.

In the second embodiment of the invention, the lower electrode 32composing the n-th nonlinear resistance element portion is connectedwith the (n+1)th anodic oxidation electrode 29 via the connectionportion 31.

Thereafter, the anodic oxidation method is applied to the tantalum filmusing the common electrode 34 as an anode, an aqueous solutioncontaining 0.01˜1.0 wt % of citric acid or ammonium borate as an anodicoxidation electrolyte and by applying a voltage at 10-20V.

Thereupon, the insulation film composed of a tantalum oxide (Ta₂O₅) filmis formed to a thickness of 35 nm on the lower electrodes 32 and theanodic oxidation electrodes 29 and 30, and the surfaces of the sidewalland topwall of the connection portions 31.

Then, as shown in FIG. 11, the chromium (Cr) film is formed to athickness of 50 nm on the upper surface of the first substrate 1 and theinsulation film 60 by use of the sputtering system. Thereafter, aphotosensitive resin is formed on the chromium film.

In the next step, by applying the etching process using thephotosensitive resin as an etching mask, each of the signal electrodes35, both made of the chromium film, is formed respectively on the anodicoxidation electrodes 29 and 30, and a pattern is formed for the firstupper electrode 36 connected with one of the signal electrodes 35 andthe second upper electrode 38 having a pad 37 connected with each of thedisplay electrodes 51.

Hereupon, the signal electrodes 35 are connected with the inputelectrodes 39 in the input terminals 40, and the chromium film is notformed on the common electrode 34.

The etching of the chromium film is carried out by the wet etchingprocess using an aqueous solution of perchloric acid and ammonium ceriumnitrate as an etchant at a temperature set in the range of 20˜30° C.

Thereafter, as shown in FIG. 12, an indium tin oxide (ITO) film as atransparent and electrically conductive film is formed to a thickness of100 nm and then, on the surface of the indium tin oxide film, aphotosensitive resin is formed.

By means of the etching process using the photosensitive resin as anetching mask, the n-th display electrode 51 connected with the n-thsignal electrode 35 composed of the indium tin oxide film via thenonlinear resistance element portion is formed.

Patterns of the display electrodes 51 are formed such that theoverlapping portion 53 where a part of the region of the connectionportion 31 connecting each of the lower electrodes 32 with the anodicoxidation electrode 29 overlaps partially each of the display electrode51 and another overlapping portion 52 where the pad 37 extended from thesecond upper electrode 38 is overlapped partially with the aforesaiddisplay electrode 51.

Further, as shown in FIG. 12, a pattern of the input electrode 54 forconnection is formed to cover the anodic oxidation electrode 30 in theinput terminal 40 at the same time when the display electrodes arepatterned.

As shown in FIG. 13, a photosensitive resin 55 is formed byphotolithographic techniques in such a way as to cover the first upperelectrode 36, the second upper electrode 38, and each of the lowerelectrodes 32.

Thereafter, as shown in FIG. 14, the connection portion 31 forconnection among the common electrode 34, the (n+1)-th anodic oxidationelectrode 29, and each of the lower electrodes 32, in an exposed region(as indicated by the phantom line in FIG. 14) other than the overlappingportion 53 is removed by the etching process using the displayelectrodes 51 and the photosensitive resin 55 as etching masks.

Hereupon, the lower electrodes 32 each resembling an island in shape areformed by separating the connection portion 31 from respectively theanodic oxidation electrode 29 and the lower electrodes 32 by the etchingprocess.

At the same time, each of the lower electrodes 32 in an exposed region32 a (as indicated by the phantom line) not covered by thephotosensitive resin 55, on the opposite side of the connection portion31, is also removed by the etching process. In this connection, thephotosensitive resin film 55 may be patterned not to have the exposedregion 32 a.

Thus the first nonlinear resistance element 62 comprising the lowerelectrode 32 resembling an island in shape, separated from the (n+1)-thanodic oxidation electrode 29, the insulation film 60, and the firstupper electrode 36 connected with the n-th signal electrode 35 isformed.

Also, the second nonlinear resistance element 63 comprising the lowerelectrode 32 resembling an island in shape, the insulation film 60, andthe second upper electrode 38 connected with the n-th display electrode51 via the pad 37 is formed.

Further, one end of each of the signal electrodes 35 is connected witheach of the input terminals 40. In each of the input terminals 40, ninput electrode 39 composed of the chromium film formed on the anodicoxidation electrode 29 or 30, and an input electrode 54 for connection,composed of a transparent and electrically conductive film formed on theinput electrode 39, can be formed.

External signals are applied on one of the display electrodes 51 via theinput portion 40—the signal electrode 35—the first nonlinear resistanceelement 62—the second nonlinear resistance element 63.

As shown in FIGS. 14 and 15, each of the display electrodes 51 isprovided with the overlapping portion 53 overlapping with the connectionportion 31 connecting each of the lower electrodes 32 with the anodicoxidation electrode 29 or 30.

When removing the connection portion 31 by the etching process, thedisplay electrodes 51 are used as etching masks. Accordingly, theconnection portion 31 is split in the exposed region (as indicated bythe phantom line in FIG. 14) where it is not overlapped with the displayelectrodes 51 so that the lower electrode 32 resembling an island inshape can be formed.

With adoption of the method of manufacturing the active substrateaccording to the second embodiment of the invention, the nonlinearresistance elements having an excellent symmetrical characteristic canbe manufactured.

Thus the d-c component of a voltage applied on the liquid crystal layeris eliminated, preventing the occurrence of the after-image phenomenonwhich poses a problem with the quality of images displayed while thedisplay electrodes 51 can be utilized as etching masks.

Accordingly, as shown in FIG. 13, when separating the anodic oxidationelectrode 29 from the lower electrode 32, it is sufficient to only formthe photosensitive resin 55 in a region over the two upper electrodes 36and 38, and one of the lower electrodes 32. This has made it possible torelax requirements for accuracy in positioning a region for thephotosensitive resin film 55 from the same in the past.

Furthermore, as a part of the connection portion 31, still remainingunder the display electrode 51, is composed of a metal film, it cantherefore shield light.

Accordingly, the remaining part of the connection portion 31 can used asa shielding against light when used in a transmissive liquid crystaldisplay, enabling partial shielding of light on the first substratecomposing the nonlinear resistance element portion.

Third Embodiment

Referring to FIGS. 16 and 17, the structure of the liquid crystaldisplay according to a third embodiment of the invention and the methodof manufacturing the same are described hereafter.

FIGS. 16 and 17 are plan views showing a part of the region of theliquid crystal display for describing the structure of the liquidcrystal display according to the third embodiment of the invention andthe method of manufacturing the same, corresponding to respectivelyFIGS. 13 and 14 used for describing the second embodiment of theinvention.

Firstly, the structure of the liquid crystal display according to thethird embodiment of the invention is described with reference to FIG.17.

A nonlinear resistance element portion disposed between one of signalelectrodes 35 and each of display electrodes 51 comprises a firstnonlinear resistance element 62 composed of a first upper electrode 36made of a chromium film, an insulation film made of a tantalum oxidefilm, and each of lower electrodes 32 made of a tantalum film.

Also, the nonlinear resistance element portion comprises a secondnonlinear resistance element 63 composed of the aforesaid lowerelectrode 32 made of the tantalum film, the insulation film 60 made ofthe tantalum oxide film, and a second upper electrode 38 made of thechromium film.

As shown in FIG. 16, the lower electrode 32 is connected with one ofanodic oxidation electrodes 29 via one of connection portions 31, andparts of the lower electrode 32, in regions outside the first upperelectrode 36 and the second upper electrode 38, are removed such thatthe opposite ends thereof are flush with the external side of the twoupper electrodes 36 and 38, respectively.

However, a middle part of each of the lower electrodes 32, between thefirst upper electrode 36 and the second upper electrode 38, is leftintact.

One end of each of the anodic oxidation electrodes 29 and 30, isconnected with a common electrode 34, and the other end with each of theinput terminals 40.

An insulation film composed of a tantalum oxide film formed by theanodic oxidation of the lower electrodes 32 is provided on the surfacesof the lower electrodes 32.

Further, a chromium film is formed on the upper surface of each of theanodic oxidation electrodes 29 and 30, constituting signal electrodes 35composed of a double layer film consisting of the tantalum film and thechromium film.

One of the signal electrodes 35 is provided with an extended portioncrossing each of the lower electrodes 32 and serving as the first upperelectrode 36 disposed on the lower electrode 32.

The second upper electrode 38 crossing each of the lower electrodes 32and disposed on the lower electrode 32 is connected with each of thedisplay electrodes 51 via a pad 37. The second upper electrode 38 isalso composed of the chromium film. The display electrodes 51 arecomposed of a transparent and electrically conductive film made ofindium tin oxide and the like.

Each of connection portions 31 connecting the lower electrodes 32 withthe anodic oxidation electrodes 29 is provided with an overlappingportion 53 partially overlapped by each of the display electrodes 51.However, an insulation film is interposed between the display electrodes51 and the connection portions 31.

The overlapping portion 53 is as wide as about a half of the width ofthe connection portion 31, and a part of the connection portion 31, in aregion exposed from the display electrode 51 as shown in FIG. 16, isdenoted as an exposed region 57.

By removing the exposed region 57 after the display electrodes 51 areformed, the lower electrode 32 resembling an island in shape isseparated from the anodic oxidation electrode 29.

Furthermore, in each of the input terminals 40, an input electrode 39composed of a chromium film and an input electrode 54 for connection,composed of a transparent and electrically conductive film, areprovided.

As a result, the first nonlinear resistance element 62 provided betweenone of the signal electrodes 35 and one of the display electrodes 51 hasa structure consisting of a chromium film—a tantalum oxide film—atantalum film while the second nonlinear resistance element 63 has astructure consisting of a tantalum film—a tantalum oxide film—a chromiumfilm.

Accordingly, connection from the signal electrode 35 to each of thedisplay electrodes 51 at one of the nonlinear resistance elements, andconnection from the aforesaid display electrode 51 to the signalelectrode 35 at the other of the nonlinear resistance elements becomestructurally symmetrical to each other.

Consequently, the nonlinear resistance elements having an excellentsymmetrical characteristic are obtained and a d-c voltage componentimpressed on a liquid crystal layer during driving can be eliminated,preventing the occurrence of the after-image phenomenon posing a problemwith displaying images.

Now referring to FIGS. 16 and 17, the method of manufacturing the liquidcrystal display according to the third embodiment of the invention isdescribed.

Firstly, a tantalum (Ta) film is formed to a thickness of 100 nm on theentire surface of a first substrate made of an insulator by use of thesputtering system. Thereafter a photosensitive resin (not shown) isformed on the tantalum film.

Then, by means of the etching process, patterns are formed for the lowerelectrodes 32, the anodic oxidation electrode 29 connected with one ofthe lower electrodes 32 via the connection portion 31, the other anodicoxidation electrode 30, the common electrode 34 connected with theanodic oxidation electrodes 29 and 30, and the input terminals 40 forinputting scanning signals sent out from the external circuit. Theetching of the tantalum film is carried out by use of the RIE system.

FIG. 16 shows the anodic oxidation electrode 30 representing a n-thscanning electrode and the anodic oxidation electrode 29 representing a(n+1)-th scanning electrode. In this embodiment of the invention, thelower electrode 32 of the n-th nonlinear resistance element is connectedwith the (n+1)-th anodic oxidation electrode 29 via the connectionportion 31.

Thereafter, the anodic oxidation method is applied to the tantalum filmusing the common electrode 34 as an anode, and an aqueous solutioncontaining citric acid or ammonium borate as an anodic oxidationelectrolyte.

Thereupon, the insulation film composed of a tantalum oxide Ta₂O₅) filmis formed to a thickness of 35 nm on the lower electrodes 32, the anodicoxidation electrodes 29 and 30, and the surfaces of the sidewall andtopwall of each of the connection portions 31.

Then, a chromium (Cr) film is formed to a thickness of 50 nm on thesurfaces of a first substrate and the insulation film by use of thesputtering system. Then, a photosensitive resin is formed on thetantalum film.

Thereafter, by means of the etching method applied to the chromium film,a pattern is formed on the anodic oxidation electrodes 29 and 30, forthe signal electrodes 35, the first upper electrode 36 connected withone of the signal electrodes 35, and the second upper electrode 38having a pad 37 connected with each of the display electrodes 51.

At the same time, the input electrode 39 made of a chromium film isformed such that the signal electrode 35 is connected with the inputelectrode 39 in each of the input terminals 40. At this time, thechromium film is not formed on the common electrode 34.

In the next step, an indium tin oxide (ITO) film as a transparent andelectrically conductive film is formed on the entire surface to athickness of 100 nm by means of the sputtering method. Thereafter, aphotosensitive resin film is formed on the indium tin oxide film.

Then, using the photosensitive resin as an etching mask, the etching ofthe indium tin oxide film is carried out by use of the RIE system, and apattern is formed for the n-th display electrode 51 connected with then-th signal electrode 35 via the nonlinear resistance element.

Furthermore, by means of the photo etching method, a pattern is formedsuch that each of the display electrodes 51 is provided with anoverlapping portion 53 where the display electrode 51 overlaps a part ofthe region for the connection portion 31 connecting each of the lowerelectrodes 32 with the anodic oxidation electrode 29, and also with anoverlapping portion 52 where the display electrode 51 overlaps a part ofthe region for the pad 37 of the second upper electrode 38.

At this time, the overlapping portion 53 is so formed as to have a widthabout half of that of the connection portion 31, and a part of theconnection portion 31, in a region exposed from the display electrode51, is denoted as an exposed region 57.

At the same time, by patterning on the transparent and electricallyconductive film, the input electrodes 54 for connection, covering theanodic oxidation electrodes 29 and 30, are formed in the input terminals40.

Thereafter, a pattern is formed by photolithographic techniques for aphotosensitive resin 71 in such a way to cover about half of the regionfor the first upper electrode 36 over the lower electrode 32, about halfof the region for the second upper electrode 38, and a part of the lowerelectrode 32 in a region between the first upper electrode 36 and thesecond upper electrode 38.

Then, by means of the etching method with the RIE system using thephotosensitive resin film 55 and the display electrodes 51 as etchingmasks, the exposed region 57 of the connection portion 31 connectingtogether the common electrode 34, the (n+1)-th anodic oxidationelectrode 29, and the lower electrode 32 is removed as shown in FIG. 17.

When the etching method is applied as above, the photosensitive resin71, the display electrodes 51, the first upper electrode 36, and thesecond upper electrode 38 serve as etching masks.

Accordingly, owing to a side 72 on the left hand of the first upperelectrode 36 and a side 73 on the right hand of the second upperelectrode 38, the lower electrode 32 and the insulation film are formedto match self-alignment with respectively the first upper electrode 36and the second upper electrode 38.

With adoption of the method of manufacturing the first substratecomposing the MIM element according to the third embodiment of theinvention as described above, nonlinear resistance elements having anexcellent symmetrical characteristic can be manufactured.

Accordingly, a d-c voltage component impressed on the liquid crystallayer can be eliminated while the display electrodes 51 can be used asetching masks.

Therefore, when separating the anodic oxidation electrodes 29 and 30from the lower electrode 32, it is sufficient to only form thephotosensitive resin 71 over the first upper electrode 36, the secondupper electrode 38, and an upper surface of the lower electrode 32between the first upper electrode 36 and the second upper electrode 38.

Furthermore, it is unnecessary to cover the entire surface of therespective first upper electrode 36 and the second upper electrode 38with the photosensitive resin 71. As a result, it has become possible torelax requirements for accuracy in positioning a region for thephotosensitive resin 71 from that in the past.

In addition, part of the connection portion 31, remaining intact underthe display electrode 51, is made of a metal film and able to shieldlight. Accordingly, when the liquid crystal display is used as atransmissive liquid crystal display, the remaining part of theconnection portion 31 can be used as a shielding against light so thatpartial shielding of light on the substrate composing the nonlinearresistance elements becomes possible.

Fourth Embodiment

Now, the structure of the liquid crystal display according to a fourthembodiment of the invention and the method of manufacturing the same aredescribed hereafter with reference to FIGS. 18 to 20.

Firstly, the structure of the liquid crystal display according to thefourth embodiment is described.

An anodic oxidation electrode 3, lower electrodes 2, and connectionportions 4 all of which are composed of a metal film made of tantalum(Ta) containing nitrogen (N), are formed on a first substrate 1, thatis, an active substrate on which nonlinear resistance elements areformed.

One end of the anodic oxidation electrode 3 is connected with a commonelectrode 6, and the other end with an input terminal 7 for applyingsignals from an external circuit to the nonlinear resistance elements.The common electrode 6 is used as an electrode for forming an insulationfilm 8 by means of the anodic oxidation method.

Further, as shown in FIG. 20, the insulation film 8 composed of anitrogen-bearing tantalum oxide (Ta₂O₅: N) film formed by the anodicoxidation of the lower electrodes 2 is provided on each of the lowerelectrodes 2.

Then, a transparent and electrically conductive film serving as a signalelectrode 9 is formed on the anodic oxidation electrode 3. A first upperelectrode 10 connected with the signal electrode 9 and a second upperelectrode 11 connected with each of display electrodes 12 are providedon each of the lower electrodes 2.

The first upper electrode 10 and the second upper electrode 11 areprovided on the lower electrode 2 with the insulation film 8 interposedin between. The lower electrode 2, the insulation film 8, and the firstupper electrode 10 constitute a first nonlinear resistance element 13,and the lower electrode 2, the insulation film 8, and the second upperelectrode 11 constitute a second nonlinear resistance element 14.

Herein, the signal electrode 9, the first upper electrode 10, the secondupper electrode 11, and the display electrodes 12 are composed of atransparent and electrically conductive film, for example, an indium tinoxide (ITO) film.

Further, the signal electrode 9 for connection with an external circuitis connected with the input terminal 7.

Each of the display electrodes 12 is provided with an overlappingportion partially overlapping with each of the connection portions 4connecting the anodic oxidation electrode 3 with each of the lowerelectrodes 2, in a region substantially resembling the letter L.

A part of each of the connection portions 4, between each of the lowerelectrodes 2 and each of the display electrodes 12, and the same betweenthe anodic oxidation electrode 3 and each of the display electrodes 12are removed, forming each of the lower electrodes 2, resembling anisland in shape.

Then, an overcoating insulation film 85 is formed on the entire surfaceof the aforesaid electrodes and the connection portions 4, and openings80 and 81 are provided on the overcoating insulation film 85 such thatthe overlapping portions 15 and the input terminal 7 are exposed.

In this embodiment, the first nonlinear resistance element 13 and thesecond nonlinear resistance element 14, provided in a region between thesignal electrode 9 and the display electrodes 12, are composed of “anindium tin oxide film—a nitrogen-bearing tantalum oxide film—anitrogen-bearing tantalum film” and “a nitrogen-bearing pantalum film—anitrogen-bearing tantalum oxide film—an indium tin oxide film”,respectively.

This means that an electric current path is provided between the signalelectrode 9 and each of the display electrodes 12 such that electriccurrent flows from “the indium tin oxide film—the nitrogen-bearingtantalum oxide film—the nitrogen-bearing tantalum film” of the firstnonlinear resistance element 13 to “the nitrogen-bearing tantalumfilm—the nitrogen-bearing tantalum oxide film—the indium tin oxide film”of the second nonlinear resistance element 14.

As a result, connection from the signal electrode 9 to each of thedisplay electrodes 12 at one of the nonlinear resistance elements, andconnection from the aforesaid display electrode 12 to the signalelectrode 9 at the other of the nonlinear resistance elements becomessymmetrical to each other.

Now, the method of manufacturing the liquid crystal display according tothe fourth embodiment of the invention is described hereafter.

As shown in FIG. 18, a nitrogen(N)-bearing tantalum (Ta) film is formedon the entire surface of the first substrate 1 to a thickness of 250 nmby the sputtering method. Thereafter, a photosensitive resin is formedon the nitrogen-bearing tantalum film.

Then a pattern is formed for the anodic oxidation electrode 3, the lowerelectrodes 2, and the connection portions 4 connecting the anodicoxidation electrode 3 with the lower electrodes 2, all of which arecomposed of a nitrogen-bearing tantalum film, by the photo etchingmethod using the photosensitive resin as an etching mask. The etching ofthe nitrogen-bearing tantalum film is carried out by use of the RIEsystem.

One end of the anodic oxidation electrode 3 is connected with the commonelectrode 6 and the other end with the terminal 7 for applying signalsfrom the external circuit on the nonlinear resistance elements.

Thereafter, an insulation film 8 composed of a nitrogen-bearing tantalum(Ta₂O₅: N) film is formed on the surface of each of the lower electrodes2 by the anodic oxidation method using the common electrode 6 as anelectrode.

Then, an indium tin oxide (ITO) film as a transparent and electricallyconductive film is formed on the entire surface to a thickness of 100 nmby the sputtering method. Subsequently, a photosensitive resin is formedon the indium tin oxide film for patterning.

The signal electrode 9 formed on the anodic oxidation film 3, the firstupper electrode 10 connected with the signal electrode 9, the displayelectrodes 12 and the second upper electrode 11 connected with each ofthe display electrodes 12 are provided by applying the etching method tothe indium tin oxide film.

Thereby each of the lower electrodes 2, the insulation film 8, and thefirst upper electrode 10 constitute the first nonlinear resistanceelement 13, and the aforesaid lower electrode 2, the insulation film 8,and the second upper electrode 11 constitute the second nonlinearresistance element 14.

The first nonlinear resistance element 13 and the second nonlinearresistance element 14 constitute a nonlinear resistance element portion.

The first upper electrode 10, the second upper electrode 11, the signalelectrode 9, and the display electrodes 12 are all made of a transparentand electrically conductive film, for example, an indium tin oxide (ITO)film, or a thin metal film.

Further, the signal electrode 9 for connection with the external circuitis connected with the input terminal 7.

Each of the display electrodes 12 is provided with the overlappingportion 15 where the aforesaid display electrode partially overlaps eachof the connection portions 4 connecting the anodic oxidation electrode 3with each of the lower electrodes 2.

In the next step, a tantalum oxide film serving as an overcoatinginsulation film for the nonlinear resistance element portion is formedon the entire surface to a thickness of 150 nm by the sputtering method.

Then a photosensitive resin is formed on the tantalum oxide film, andpatterning on the photosensitive resin is provided by photolithographictechniques using a predetermined photo mask such that openings in thephotosensitive resin correspond to the openings 80 and 81.

Then, by etching the tantalum oxide film using the photosensitive resinas an etching mask, the openings 80 and 81 are formed in a region forthe overlapping portion 15 where each of the connection portions 4 ispartially overlapped with each of the display electrodes 12, and aregion for the input terminal 7, respectively.

The etching of the tantalum oxide film is carried out with the RIEsystem using a mixture of carbon tetrafluoride (CF₄) at a flow rate of200˜240 sccm and oxygen (O₂) at a flow rate of 10˜40 sccm undercondition of pressure at 4˜12×10⁻² torr and power consumption at 0.2˜0.5kW/cm².

As shown in FIG. 19, using each of the display electrodes 12 as well asthe photosensitive resin film as etching masks, the lower electrodes 2each resembling an island in shape are formed by removing parts of eachof the connection portions 4 connecting the anodic oxidation electrode 3with each of the lower electrodes 2, exposed in each of the openings 80.

In this embodiment, an overcoating insulation film 85 is formed in aregion including the nonlinear resistance element portion. Theovercoating insulation film 85 is provided with the opening 81 and theopening 80 used for separating each of the connection portionsconnecting each of the lower electrodes 2 with the anodic oxidationelectrode.

Thus each of the connection portions 4 is split by the etching methodusing the photosensitive resin for forming the opening 80 of theovercoating insulation film 85 and the display electrodes 12 as etchingmasks.

Accordingly, as shown in FIG. 20, the lower electrode 2 and theinsulation film 8, constituting the nonlinear resistance element, areprovided with a side 86 matching with the opening 80.

Similarly, the connection portion 4 and the insulation film 8 areprovided with a side 87, respectively, flush with the edge of thedisplay electrode 12.

As is evident from the description above, the nonlinear resistanceelement provided between the signal electrode 9 and the displayelectrodes 12 comprises the first nonlinear resistance element 13composed of “an indium tin oxide film—a nitrogen-bearing tantalum oxidefilm—a nitrogen-bearing tantalum film” and the second non-linearresistance element 14 composed of “a nitrogen-bearing tantalum film—anitrogen-bearing tantalum oxide film—an indium tin oxide film”.

As a result, connection from the signal electrode 9 to each of thedisplay electrodes 12 at one of the nonlinear resistance elements, andconnection from the aforesaid display electrode 12 to the signalelectrode 9 at the other of the nonlinear resistance elements becomestructurally symmetrical to each other.

Accordingly, by adoption of the fourth embodiment of the invention, thenonlinear resistance elements having a symmetrical current-voltagecharacteristic can be obtained.

Therefore, a d-c voltage component applied on a liquid crystal layerduring driving operation is nearly eliminated, and the waveform of avoltage applied on the signal electrode can be made symmetrical.

Consequently, a d-c voltage component is applied neither between thesignal electrode 9 and the display electrodes 12 nor between the signalelectrode 9 and opposite electrodes, preventing the occurrence of theafter-image phenomenon that poses a problem with displaying images.

Therefore, a liquid crystal display having an excellent display qualityis obtained. Furthermore, by forming the overcoating insulation film 85on the nonlinear resistance elements, variation with time in theperformance of the nonlinear resistance elements can be held to aminimum.

As the formation of the overcoating insulation film 85 requires removalthereof at the input terminal 7 for connection with the externalcircuit, the opening 81 is provided.

Also, in this embodiment, it is unnecessary to form an etching maskadditionally for separating the connection portion 4 between each of thelower electrodes 2 and the anodic oxidation electrode 3, and aseparating process is much simplified.

Other Embodiment

Now, referring to FIGS. 21 and 22, a liquid crystal display according toan embodiment different from the first through the fourth embodiment ofthe invention is described hereafter.

An constitution as shown in FIGS. 21 and 22 is different from that ofthe liquid crystal display according to the first through the fourthembodiment of the invention only with respect to the number of the upperelectrodes.

In the embodiment as shown in FIGS. 21 and 22, four upper electrodes,that is, a first upper electrode 91, a second upper electrode 92, athird upper electrode 93, and a fourth upper electrode 94 are providedto cross one of the lower electrodes 2 thereon while two upperelectrodes are provided in the first through the fourth embodiment.

In the embodiment as shown in FIG. 21, the first upper electrode 91 andthe third upper electrode 93 are connected with the signal electrode 9while the second upper electrode 92 and the fourth upper electrode 94are connected with the display electrodes 12.

This means that in this constitution, the first upper electrode 91 andthe third upper electrode 93 are connected in parallel, and the secondupper electrode 92 and the fourth upper electrode 94 are connected inparallel. Then, upper electrodes connected in parallel are connectedwith in series other upper electrodes connected in parallel.

The liquid crystal display as shown in FIG. 21 has an effect ofcompensating for malfunctioning of the nonlinear resistance elementportion due to a break occurring therein in addition to the effect ofreducing a d-c voltage component of a voltage applied, attributable tothe asymmetrical current-voltage characteristic so that display withoutthe after-image phenomenon is obtained, as described in the foregoing.

In the constitution shown in FIG. 22, the first upper electrode 91, thesecond upper electrode 92, the third upper electrode 93, and the fourthupper electrode 94 are connected in series.

And, the liquid crystal display as shown in FIG. 22 has an effect ofallowing the insulation film on respective nonlinear resistance elementsto be made thinner in addition to the effect of reducing a d-c voltagecomponent of a voltage applied, attributable to the asymmetricalcurrent-voltage characteristic, so that display without the after-imagephenomenon is obtained, as described in the foregoing.

Further, in FIGS. 21 and 22, the embodiment wherein four upperelectrodes are provided is described. However, six or more upperelectrodes may be provided as long as the upper electrodes are in aneven number. The method of manufacturing the liquid crystal displayaccording to the first through the fourth embodiment may be applied formanufacturing the other embodiment described above.

In the aforesaid embodiments of the invention, examples wherein indiumtin oxide (ITO) is used for the transparent and electrically conductivefilm are described. Alternatively, other oxides such as indium oxide(In₂O₃), tin oxide (SnO₂), zinc oxide (ZnO) or the like may be used.

Also, examples wherein tantalum or tantalum containing nitrogen is usedfor the lower electrode are described. Alternatively, a metal film madeof tantalum containing carbon, silicon, niobium, or aluminum may beused.

Further, in the second and the third embodiments, an example wherein achromium film is used for the upper electrode is described. Again,alternatively, a metal film other than the chromium film such as achromium film containing titanium, tungsten, titanium silicide, tungstensilicide, or nitrogen may be used as well.

Fifth Embodiment

Referring to FIGS. 23 and 24, a fifth embodiment of the invention isdescribed hereafter.

FIG. 23 is a plan view showing a part of a region for a first substrateon which nonlinear resistance elements (MIM elements) of a liquidcrystal display according to the fifth embodiment of the invention. FIG.24 is a sectional 1 view taken along the line XXIV—XXIV of FIG. 23.Referring to said figures, the constitution of the liquid crystalaccording to this embodiment is described hereafter.

Anodic oxidation electrodes 3, lower electrodes 2, connection portions4, each connecting each of the anodic oxidation electrode 3 with twolower electrodes 2 and 2, all of which are composed of a metal film madeof tantalum, are provided on a transparent substrate 1 of activesubstrate on which the nonlinear resistance elements are formed. Each ofthe connection portions 4 is provided with a T-shaped part 4 a where anoverlapping portion 15, resembling the letter T in shape, is formedunder each of display electrodes 95 described hereafter.

One end of each of the anodic oxidation electrodes 3 is connected with acommon electrode 6, and the other end with an input terminal 7 forapplying signals from an external circuit on the nonlinear resistanceelements. The common electrode 6 serves as an electrode when the anodicoxidation method is applied to the surface of each of the lowerelectrodes 2 for forming an insulation film 8 thereon.

Now, arrangement of the anodic oxidation electrodes 3, the overlappingportions 15, the lower electrodes 2, and the connection portions 4 isdescribed.

As shown in FIG. 23, each of the overlapping portions 15, resembling theletter T in shape, provided underneath each of the display electrodes 95is connected with the anodic oxidation electrode 3 via each of theconnection portions 4 on one side of the T-shaped part 4 a, and with thetwo lower electrodes 2 via the connection portion 4 on two sides of theT-shaped part 4 a crossing the aforesaid one side thereof at rightangles. Further, a plurality of the anodic oxidation electrodes 3 areconnected with each other via the common electrode 6 in an externalregion.

In the construction adopted for the liquid crystal display, a part ofeach of the connection portions 4, between the signal electrode 9 andthe display electrode 95, and other parts thereof between the T-shapedpart 4 a and the two lower electrodes 2 are separated.

The connection portion 4 between the signal electrode 9 and the displayelectrode 95 has one side substantially matching with the displayelectrode 95, and the connection portions 4 between the overlappingportion 15 resembling the letter T in shape and the two lower electrodes2 have also sides substantially matching with the display electrode 95.Further, the common electrode 6 connected with the signal electrode 9 isalso separated from the signal electrode 9.

Regions indicated by dash and double dotted lines covering theconnection portion 4 between the anodic oxidation electrode 3 oppositethe signal electrode 9 and the display electrode 95 provided with theoverlapping portion 15, the connection portions 4 between theoverlapping portion 15 resembling the letter T in shape and the twolower electrodes 2, and the common electrode 6 show the condition of anintermediate step in a process of manufacturing the liquid crystaldisplay.

Further, the display electrode 95 provided with the overlapping portion15 and the display electrode 96 without the overlapping portion 15 arealternately disposed against the signal electrode 9.

The insulation film 8 composed of a tantalum oxide (Ta₂O₅) film formedby applying the anodic oxidation method to the lower electrode 2 isprovided on the surface of the lower electrode 2.

A transparent and electrically conductive film is formed on each of theanodic oxidation electrodes 3 and is used as the signal electrode 9. Afirst upper electrode 10 connected with the signal electrode 9, and asecond upper electrode 11 connected with the display electrode 95 areprovided on each of the lower electrodes 2 so as to cross the lowerelectrode 2.

The first upper electrode 10 and the second upper electrode 11 areprovided on the aforesaid lower electrode 2 resembling an island inshape with the insulation film 8 interposed in-between.

A first nonlinear resistance element 13 is composed of the lowerelectrode 2, the insulation film 8 and the first upper electrode 10, anda second nonlinear resistance element 14 is composed of the lowerelectrode 2, the insulation film 8 and the second upper electrode 11.

Herein the signal electrodes 9, the first upper electrodes 10, thesecond upper electrodes 11 and the display electrodes 95 are allcomposed of a transparent and electrically conductive film, for example,an indium tin oxide (ITO) film.

Further the signal electrodes 9 for connection with an external circuitare connected with an input terminal 7.

Herein, the first nonlinear resistance element 13 and the secondnonlinear resistance element 14, provided in a region between the signalelectrode 9 and the display electrode 95 or 96, are composed of “anindium tin oxide film—a tantalum oxide film—a tantalum film” and “atantalum film—a tantalum oxide film—an indium tin oxide film”,respectively.

This means that an electric current path is provided between the signalelectrode 9 and the display electrodes 95 or 96 such that electriccurrent flows from “the indium tin oxide film—the tantalum oxidefilm—the tantalum film” of the first nonlinear resistance element 13 to“the tantalum film—the tantalum oxide film—the indium tin oxide film” ofthe second nonlinear resistance element 14.

As a result, connection from the signal electrode 9 to the displayelectrodes 95 or 96 at one of the nonlinear resistance elements, andconnection from the display electrode 95 or 96 to the signal electrode 9at the other of the nonlinear resistance elements become symmetrical toeach other.

As is evident from the description as above, a proportion of the areafor the overlapping portion 15 can be reduced since the displayelectrode 95 provided with the overlapping portion 15 overlaps with theT-shaped part 4 a of the connection portion 4 and the display electrode96 without the overlapping portion 15 are alternately disposed.

Consequently, the liquid crystal display according to this embodiment iscapable of giving a brighter display in comparison with a case whereineach of the display electrodes is provided with an overlapping portion15.

Sixth Embodiment

Referring to FIGS. 25 and 26, a liquid crystal display according to asixth embodiment of the invention is described. FIG. 25 is a plan viewshowing a part of a region for a first substrate on which nonlinearresistance elements (MIM elements) of a liquid crystal display accordingto the sixth embodiment of the invention is formed. FIG. 26 is asectional view taken along the line XXXI—XXXI of FIG. 25.

In this liquid crystal display, four display electrodes, 95, 95, 96, and96, constitute one pixel. With adoption of this constitution,malfunction of a pixel can be prevented even when a non-linearresistance element of one of the display electrodes malfunctions as longas three other display electrodes are functioning normally.

Furthermore, an improvement on a viewing angle characteristic of theliquid crystal display can be achieved by adoption of a system wherebyeach of the four display electrodes is provided with the nonlinearresistance element having a different “current-voltage characteristic”by, for example, varying an area of the nonlinear resistance elementsfor each of the display electrodes.

Anodic oxidation electrodes 3, lower electrodes 2, connection portions4, each connecting each of the anodic oxidation electrode 3 with twolower electrodes 2 and 2, and provided with a T-shaped part 4 a, all ofwhich are composed of a metal film made of aluminum, are provided on atransparent substrate 1, that is, an active substrate on which thenonlinear resistance elements are formed.

The T-shaped part 4 a of the connection portion 4 forms an overlappingportion 15 under the display electrodes 95. One side of the T-shapedpart 4 a is connected with the anodic oxidation electrode 3 via theconnection portion 4. The other sides thereof connect with the two lowerelectrodes 2 via the connection portion 4.

One end of each of the anodic oxidation electrodes is connected with acommon electrode 6, and the other end with an input terminal 7 forapplying signals from an external circuit on the nonlinear resistanceelements. The common electrode 6 serves as an electrode when the anodicoxidation method is applied to the surface of each of the lowerelectrodes 2 for forming an insulation film 8 thereon.

In the construction adopted for the liquid crystal display, a part ofeach of the connection portions 4, between the signal electrode 9 andthe display electrode 95, and other parts thereof (as shown by a phantomline in FIG. 25) between the overlapping portion 15 resembling theletter T in shape and the two lower electrodes 2 are separated. Theconnection portion 4 between the signal electrode 9 and the displayelectrode 95 has one side substantially matching the display electrode95, and the connection portions 4 between the overlapping portion 15resembling the letter T in shape and the two lower electrodes 2 havealso sides substantially matching the display electrode 95. Further, thecommon electrode 6 (as shown by a phantom line in FIG. 25) connectedwith the ignal electrode 9 is also separated from the signal electrode9.

Regions indicated by phantom lines in the figure covering the connectionportion 4 between the anodic oxidation electrode 3 opposite the signalelectrode 9 and the display electrode 95 provided with the overlappingportion 15, the connection portions 4 between the overlapping portion 15resembling the letter T in shape and the two lower electrodes 2, and thecommon electrode 6 show the condition of an intermediate step in aprocess of manufacturing the liquid crystal display.

Further, the display electrode 95 provided with the overlapping portion15 and the display electrode 96 without the overlapping portion 15 arealternately disposed opposite to the signal electrode 9. Two displayelectrodes 95 and 96 are disposed symmetrically with respect to thesignal electrode 9 such that two display electrodes 95 and 95, bothprovided with the overlapping portion 15 and disposed diagonally, crosstwo display electrodes 96 and 96 without the overlapping portion 15 andalso diagonally disposed. Four display electrodes consisting of two eachof the display electrodes 95 and 96 constitute one pixel.

The insulation film 8 composed of a tantalum oxide (Ta₂O₅) film formedby applying the anodic oxidation method to the lower electrode 2 isprovided on the surface of the lower electrode 2.

A thin metal film is formed on the anodic oxidation electrodes 3 and isused as the signal electrode 9. A first upper electrode 10 connectedwith the signal electrode 9 is provided on the lower electrode 2, andfurther a second upper electrode 11 connected with the display electrode95 and 96 is provided on the aforesaid lower electrode 2.

The first upper electrode 10 and the second upper electrode 11 areprovided on the aforesaid lower electrode 2 resembling an island inshape with the insulation film 8 interposed in-between.

A first nonlinear resistance element 13 is composed of the lowerelectrode 2, the insulation film 8 and the first upper electrode 10, anda second nonlinear resistance element 14 is composed of the lowerelectrode 2, the insulation film 8 and the second upper electrode 11.

Herein the signal electrodes 9, the first upper electrodes 10, thesecond upper electrodes 11 and the display electrodes 95 and 96 are allcomposed of a thin metal film, for example, a thin niobium (Nb) film.

Further the signal electrodes 9 for connection with an external circuitare connected with an input terminal 7.

Herein, the first nonlinear resistance element 13 and the secondnonlinear resistance element 14, provided in a region between the signalelectrode 9 and the display electrode 95 or 96, are composed of “a thinniobium film—a tantalum oxide film—a tantalum film” and “a tantalumfilm—a tantalum oxide film—a thin niobium film”, respectively.

This means that an electric current path is provided between the signalelectrode 9 and the display electrodes 95 or 96 such that electriccurrent flows from “the thin niobium film—the tantalum oxide film—thetantalum film” of the first nonlinear resistance element 13 to “thetantalum film—the tantalum oxide film—the thin niobium film” of thesecond nonlinear resistance element 14.

As a result, connection from the signal electrode 9 to the displayelectrodes 95 or 96 at one of the nonlinear resistance elements, andconnection from the display electrode 95 or 96 to the signal electrode 9at the other of the nonlinear resistance elements become symmetrical toeach other.

As is evident from the description as above, the overlapping portions 15are disposed symmetrically with respect to a focal point by arrangingthe display electrode 95 having the overlapping portion 15 resemblingthe letter T in shape and the display electrode 96 not having theoverlapping portion 15, alternately, opposite to the signal electrode 9and in such a way that two display electrodes 95 and 95 diagonallydisposed across the signal electrode 9 cross two display electrodes 96and 96 similarly disposed.

As a result, the liquid crystal display provided with the displayelectrodes 96 without the overlapping portion 15 according to thisembodiment is capable of giving a brighter display in comparison withthe liquid crystal display wherein every display electrode is providedwith the overlapping portion 15.

Seventh Embodiment

Referring to FIGS. 27 and 28, a liquid crystal display according to aseventh embodiment of the invention is described. FIG. 27 is a plan viewshowing a part of a region for a substrate on which nonlinear resistanceelements (MIM elements) of a liquid crystal display according to thisembodiment is formed. FIG. 28 is a sectional view taken along the lineXXVIII—XXVIII of FIG. 27.

In this embodiment, an example wherein each of display electrodes 100 isprovided with only one nonlinear resistance element 13 is described.

Anodic oxidation electrodes 3 and lower electrodes 2 extended from eachof the anodic oxidation electrodes 3, all of which are composed of ametal film made of tantalum (Ta), are formed on a substrate 1, that is,an active substrate on which nonlinear resistance elements are formed.The anodic oxidation electrode 3 has an overlapping portion 101 underthe display electrodes 100 adjacent thereto.

An insulation film 8 composed of a tantalum oxide (Ta₂O₅) film formed byapplying the anodic oxidation method to the lower electrodes 2 is formedon the surface of each of the lower electrodes 2.

A transparent and electrically conductive film is formed on each of theanodic oxidation electrodes 3 and used as a signal electrode 9. An upperelectrode 10 connected with each of the display electrodes 100 isprovided on each of the lower electrodes 2, and a nonlinear resistanceelement 13 is composed of a nonlinear resistance layer consisting of thelower electrode 2 and the insulation film 8, and the upper electrode 10.

Herein the signal electrode 9, the upper electrode 10, and the displayelectrode 100 are all composed of a transparent and electricallyconductive film, for example, an indium tin oxide (ITO) film.

Further, the signal electrodes 9 for connection with an external circuitare connected with input terminals 7.

Now, the constitution of the anodic oxidation electrodes 3 is described.One end of each of the anodic oxidation electrodes 3 is connected with acommon electrode 6, and the other end with each of the input terminals 7for applying signals from an external circuit on the nonlinearresistance elements. The common electrode 6 serves as an electrode whenthe anodic oxidation method is applied to the surface of each of thelower electrodes 2 for forming an insulation film 8 thereon. Before theanodic oxidation method is applied, each of the anodic oxidationelectrodes 3 is provided with the overlapping portion 101 under thesignal electrode 9 and the adjacent display electrodes 100, and aconnection portion 4 consisting of a part connecting the underside ofthe signal electrode 9 with the overlapping portion 101, and anotherpart connecting together the display electrodes 100 disposed in parallelwith the signal electrode 9. Accordingly, the width of the anodicoxidation electrode 3 as indicated by a broken line is W1.

For completion of the liquid crystal display, the part of the connectionportion 4, between the underside of the signal electrode 9 and theoverlapping portion 101, and the other part thereof between the displayelectrodes 100 disposed in parallel with the signal electrode 9 areseparated, and a wiring width of the liquid crystal display in drivingcondition is made to be W2 (W2<W1). Further, each of the displayelectrodes 100 is separated from the signal electrode 9, forming astructure wherein the display electrodes 100 are connected with thesignal electrode 9 via the nonlinear resistance element 13.

Further, the connection portion 4 connecting together display electrodes100 is separated so that the display electrodes 100 are isolated fromeach other.

The common electrode 6 connected with the signal electrodes 9 is alsoseparated from the signal electrodes 9.

Uniformity in the quality and the thickness of a film formed by theanodic oxidation method is improved and also a high performance film canbe formed in a short time by providing the anodic oxidation electrode 3with the overlapping portion 101 so that the width W1 of the anodicoxidation electrode 3 is enlarged before applying the anodic oxidationmethod.

This means that the width of the anodic oxidation electrode 3 in usewhen the liquid crystal display is put to use can be made smaller byproviding the overlapping portion 101 under the display electrodes 100,resulting in a brighter display.

Furthermore, it has become possible to improve accuracy in aligningblack matrices with the display electrodes 100 by using a part of eachof the overlapping portions 101 as a black matrix for improving displayquality of a liquid crystal display.

In addition, a photosensitive resin and the display electrodes can beused as etching masks when separating the lower electrodes composing thenonlinear resistance elements from the anodic oxidation electrodes.Consequently, requirements for accuracy in aligning the photosensitiveresin film covering the connection portions with the nonlinearresistance elements can be relaxed.

As a result, the liquid crystal display according to this embodiment cancontribute to improvement of the display quality with ease. Inparticular, with respect to prevention of the image sticking phenomenon,it can have an improved characteristic as good as or better than that ofa 3-terminal type display.

Further, degradation of nonlinear resistance elements can be minimizedby covering the nonlinear resistance elements with the overcoatinginsulation film, improving the reliability of the liquid crystaldisplay.

INDUSTRIAL UTILIZATION

As described in the foregoing, by use of the liquid crystal displayprovided with nonlinear resistance elements according to the presentinvention, it is possible to turn an asymmetrical current-voltagecharacteristic of nonlinear resistance elements, due to a voltageapplied, symmetrical, and to reduce a d-c voltage component applied on aliquid crystal layer, preventing deterioration of image quality orcontrast of the liquid crystal display or a flicker phenomenon and animage sticking phenomenon, that is, an after-image phenomenon.

In addition, a photosensitive resin film and the display electrodes canbe used as etching masks when separating the lower electrodes composingthe nonlinear resistance elements from the anodic oxidation electrodes.Consequently, requirements for accuracy in aligning the photosensitiveresin covering the connection portions with the nonlinear resistanceelements can be relaxed.

As a result, the liquid crystal display according to this embodiment cancontribute to improvement of the display quality with ease. Inparticular, with respect to prevention of the image sticking phenomenon,it can have an improved characteristic as good as or better than that ofa 3-terminal type display.

Further, degradation of nonlinear resistance elements can be minimizedby covering the nonlinear resistance elements with the overcoatinginsulation film, improving the reliability of the liquid crystaldisplay.

Accordingly, the display quality of liquid crystal displays that are inwide use for various kinds of portable or small-sized electronicequipment can be enhanced and efficient manufacturing of the same isrealized.

What is claimed is:
 1. A liquid crystal display provided with displayelectrodes disposed in a matrix configuration, said display electrodesserving as pixels, comprising: a substrate comprising thereon an anodicoxidation electrode, and lower electrodes each resembling an island inshape, both of which are composed of a metal film, an insulation filmformed on the metal film, two upper electrodes composed of a transparentand electrically conductive film formed on each of the lower electrodeswith the insulation film interposed in-between, display electrodescomposed of a transparent and electrically conductive film, and signalelectrodes composed of a metal film or a metal film and a transparentand electrically conductive film; said two upper electrodes beingdisposed so as to cross each of the lower electrodes, and constitutingtwo nonlinear resistance elements in combination with the insulationfilm and the aforesaid lower electrode; said liquid crystal displaybeing characterized in that one of the two upper electrodes constitutingthe nonlinear resistance elements is connected with the signalelectrode, the other with each of the display electrodes; and thedisplay electrodes, serving as pixels, include a first display electrodeprovided with an overlapping portion having a remaining double layerfilm thereunder, composed of the same metal film as that composing thelower electrode and the insulation film, and a second display electrodenot provided with the overlapping portion.
 2. A liquid crystal displayprovided with display electrodes disposed in a matrix configuration, aplurality of the display electrodes composing one pixel, said liquidcrystal display comprising: a substrate comprising thereon an anodicoxidation electrode, and lower electrodes each resembling an island inshape, both of which are composed of a metal film, an insulation filmformed on the metal film, two upper electrodes composed of a transparentand electrically conductive film formed on each of the lower electrodeswith the insulation film interposed in-between, display electrodescomposed of a transparent and electrically conductive film, and a signalelectrode composed of a metal film or a metal film and a transparent andelectrically conductive film; said two upper electrodes being disposedso as to cross each of the lower electrodes, and constituting twononlinear resistance elements in combination with the insulation filmand the aforesaid lower electrode; said liquid crystal display beingcharacterized in that one of the two upper electrodes constituting thenonlinear resistance elements is connected with the signal electrode,the other with each of the display electrodes; and the plurality of thedisplay electrodes composing one pixel, include a first displayelectrode provided with an overlapping portion having a remaining doublelayer film thereunder, composed of the same metal film as that composingthe lower electrode and the insulation film, and a second claim 11display electrode not provided with the overlapping portion.
 3. A liquidcrystal display provided with display electrodes disposed in a matrixconfiguration, a plurality of the display electrodes composing onepixel, said liquid crystal display comprising: a substrate comprisingthereon an anodic oxidation electrode, and lower electrodes eachresembling an island in shape, both of which are composed of a metalfilm, an insulation film formed on the metal film, two upper electrodescomposed of a transparent and electrically conductive film formed oneach of the lower electrodes with the insulation film interposedin-between, display electrodes composed of a transparent andelectrically conductive film, and signal electrodes composed of a metalfilm or a metal film and a transparent and electrically conductive film;said two upper electrodes being disposed so as to cross each of thelower electrodes, and constituting two nonlinear resistance elements incombination with the insulation film and the aforesaid lower electrode;said liquid crystal display being characterized in that one of the twoupper electrodes constituting the nonlinear resistance elements isconnected with each of the signal electrodes, the other with each of thedisplay electrodes; and the plurality of the display electrodes,composing one pixel, include a first display electrode provided with anoverlapping portion having a remaining double layer film thereunder,composed of the same metal film as that composing the lower electrodeand the insulation film, and the other being the display electrode notprovided with the overlapping portion, and the nonlinear resistanceelements of the plurality of the display electrodes composing one pixelare concentrated.